A flat waveguide-type laser device has the structure in which a laser medium of a thin flat plate shape extending in a traveling direction of a laser beam is interposed between two claddings having refractive indexes lower than that of the laser medium. The laser medium functions as a waveguide.
In this flat waveguide-type laser device, the waveguide is thin and has a high excitation density. Therefore, even when a laser medium with a small cross-section for stimulated emission is used, a large gain can be obtained. This allows implementation of highly efficient amplification and/or emission operations.
Moreover, extending the waveguide in its width direction allows for scaling of output while the excitation density is maintained at a predetermined value.
On the other hand, the flat waveguide-type laser device provides a high gain and is prone to amplification and/or emission in a plurality of waveguide modes, thereby possibly causing difficulty in producing the amplification and/or emission of a laser beam of a required linear polarization. Further, it is difficult to produce the amplification and/or emission of a laser beam in a limited required mode.
In addition, it is difficult to suppress amplification of undesired light (parasitic amplification) and/or parasitic emission that occurs due to confinement of light within the waveguide by total reflections on the outer and end surfaces of the cladding, thereby causing difficulty in efficient emission of the laser beam.
To address the above, a flat waveguide-type laser device that allows for emitting a laser beam in a desired mode is proposed (e.g. refer to Patent Reference 1).
This flat waveguide-type laser device uses, as a core, a birefringent laser medium having an optical axis on a cross-section perpendicular to a light axis that is parallel to a traveling direction of the laser beam. The flat waveguide-type laser device further uses, as a material of claddings bonded to upper and lower surfaces of the laser medium, a material having a refractive index between a refractive index of the laser medium for TE polarized light and a refractive index for TM polarized light.
This prevents one of the TE and TM polarized lights from satisfying conditions for total reflections, thereby enabling laser emission of only one of these polarized lights satisfying the conditions for total reflections to emit a laser beam in a desired mode.